The present invention relates to a method for dyeing textile material with one or more fibre-reactive disperse dyestuffs in a supercritical or almost critical fluid, which textile material is selected from the group consisting of silk, wool and cellulose, combinations thereof and combinations of one or more thereof with synthetic fibres.
A dyeing method of this type for dyeing wool and wool-containing fabrics is known from the article xe2x80x9cWolle fxc3xa4rben ohne Wasser. Mxc3x6glichkeiten und Grenzen xc3xcberkritischer Fluidexe2x80x9d in DWI Reports 122 (1999). In this article, it is stated that modification of supercritical carbon dioxide with water, although increasing the solubility of a conventional wool dyestuff in the supercritical fluid and considerably increasing the dyeing, causes damage to the fibres at dyeing temperatures of over 100xc2x0 C. An increase in the temperature is desirable in order to raise the dyeing rate. Fibre-reactive disperse dyestuffs are not subject to the problem of a (too) low solubility. It is reported that the most important advantage of fibre-reactive disperse dyestuffs is that the washfastness and fastness to rubbing are good.
The dyeing of textile materials in a supercritical fluid per se is already known from DE-A1-39 06 724. In this known method according to DE-A1-39 06 724, a supercritical fluid which contains one or more dyestuffs is made to flow onto and through a textile substrate which is to be treated. The type of fluid is in this case selected as a function of the dyeing system, which system is determined by the type of dyestuff and the type of textile material. Optionally modified polar (dipolar) supercritical fluids or mixtures thereof are selected for polar dyeing systems, such as water-soluble reactive dyestuffs, acid dyestuffs and basic dyestuffs. One example of a modifying agent for changing the polarity of supercritical CO2 is water, so that the dyestuff used dissolves better in the supercritical fluid. Nonpolar fluids are used for nonpolar dyeing systems, such as disperse dyestuff systems. For textile materials which contain both nonpolar and polar fibres and are therefore dyed using different types of dyestuffs, it is proposed in DE-A-39 06 724 for these materials to be dyed in a plurality of steps, each step using a system of dyestuff and supercritical fluid which is suitable for one type of fibre. CO2 as nonpolar supercritical fluid gives good results for dyeing textile materials made from the synthetic fibres of polyester and acetate using disperse dyestuffs, as is also described DE-A1-43 32 219. It is assumed that carbon dioxide dissolves in hydrophobic fibres of the textile material, such as the abovementioned polyester and acetate fibres, with the result that these fibres swell (cf. EP-B1-0 222 207, in which this effect is described), so that the uptake of the disperse dyestuff is improved. However, the above technique cannot readily be used for hydrophilic fibres, such as wool, silk and cellulose (cotton, viscose) fibres, with the conventional water-soluble acid or reactive dyestuffs or with disperse dyestuffs. To make it possible to dye textile materials which contain wool, silk or cellulose, if desired in combination with synthetic fibres such as polyamide fibres or polyester fibres, for this purpose it is proposed in the abovementioned DE-A1-43 32 219 for the textile materials to be pretreated with a hydrophobic finishing agent (xe2x80x9cAusrxc3xcstmittelxe2x80x9d) prior to the dyeing in supercritical CO2 with a disperse dyestuff. This pretreatment can be carried out as a separate step by bringing the textile material Into contact with an aqueous solution of the finishing agent, if desired with heating, after which the pretreated textile material is thoroughly pressed and dried under conditions which are such that the hydrophobic finishing agent cures or crosslinks with the fibre. The pretreatment with the finishing agent may also be carried out directly in an autoclave in an atmosphere of supercritical CO2. However, the washfastness and fastness to rubbing of textile materials which have been pretreated in this way and dyed are lower than the fastnesses which are required and can be achieved with the conventional acid or reactive dyestuffs which have been dissolved in water. This shortcoming is described in DE-A1-44 22 707. Incidentally, it is pointed out here that acid and alkaline dyestuffs do not form a covalent bond, but rather a much weaker ionic bond. When textile which has been dyed with dyestuffs of this type is rinsed or washed, contamination is released on account of the poor fixation of the dyestuffs to the textile. According to the dyeing method which is described in this latter application, for dyeing cellulose-containing substrates with fibre-reactive disperse dyestuffs in supercritical CO2, the substrate is previously modified with compounds which contain amino groups, with the result that even and colourfast colours with good washfastness and fastness to rubbing are obtained. The fibre-reactive disperse dyestuffs used are dyestuffs which in addition to the fibre-reactive group do not contain any group which makes them soluble in water, and the fibre-reactive group itself is not or does not comprise a group which makes the dyestuff soluble in water. The term xe2x80x9cfibre-reactivexe2x80x9d in general refers to those molecule parts which can react and form a covalent bond with hydroxyl groups, for example of cellulose, or with amino and thiol groups, for example of wool and silk, of synthetic polymers, such as polyamides, and with amine-treated cellulose. The dyestuff therefore reacts with the fibres, so that a covalent bond is formed between the dyestuff and the fibre. A fibre-reactive disperse dyestuff of this type can be well fixed in cellulose and polyester materials on the basis of the chemical structure. However, the fixation of the dyestuff in polyester material is based on the penetration of the dyestuff into swollen polyester fibres, the dyestuff being mechanically xe2x80x9canchoredxe2x80x9d in the fibre when the swelling is eliminated at the end of the dyeing process. In the method described in the examples of DE-A1-44 22 707, a cotton-containing fabric is pretreated in accordance with a procedure which is known from EP-A1-0 546 476 and is then dried, after which the supercritical dyeing is carried out in an autoclave in which a dyestuff and a quantity of solid CO2 are placed.
Currently, an increasing number of textile materials are being demanded and developed which are composed of different materials, for example purely of natural fibre materials, such as 80% cotton with the addition of 20% silk or wool, or combinations of natural fibre materials of this type with synthetic fibre materials, such as polyester and polyamide.
It has therefore been found that there is still a need for improvements and/or simplifications to the methods for dyeing textile materials in a supercritical fluid, in particular for combined textile materials which contain natural fibres, in particular based on cellulose (cotton, viscose).
It is an object of the present invention to provide a relatively simple and inexpensive method for dyeing a wide range of materials which contain at least one of the textile materials cellulose, wool or silk using one or more fibre-reactive disperse dyestuffs, resulting in colourfastnesses and washfastnesses which are comparable to or better than those achieved with reactive dyestuffs which are normally used for dyeing in water.
According to the invention, to this end the method of the type described in the introductory part is characterized in that the relative humidity of the fluid is in the range from 10-100% during dyeing.
The term supercritical fluid is understood as meaning a fluid in which the pressure and/or the temperature is/are above the critical pressure and/or critical temperature which is/are characteristic of the fluid in question. Examples of supercritical fluids which can possibly be used include, inter alia, CO2, N2O, the lower alkanes, such as ethane and propane, and mixtures thereof. In practice, the explosion limits and toxicity values also play an important role in the composition of the fluid.
The dyeing method according to the present invention is carried out under supercritical or almost critical conditions. This is contrary to WO 97/1743, wherein a continuous process for the application of textile treatment compositions to textile materials is disclosed. Therein the textile treatment composition such as a dipolar water soluble CI dye is dissolved in a supercritical fluid, however the application itself occurs under atmospheric conditions.
When carrying out the method according to the invention, it is ensured that a quantity of water is present and remains in the supercritical fluid, so that the relative humidity of the fluid lies between 10% and 100%, 100% representing the maximum molecular solubility of water in the supercritical fluid. If the relative humidity of the fluid is below 10%, the natural textile materials are too dry, and consequently the uptake of the dyestuff leaves something to be desired. It has even been found that dry CO2 is capable of extracting some of the moisture which is naturally present in the textile materials, making the fibres less accessible to the dyestuff so that they are not dyed or are only slightly dyed. These natural, normal moisture contents for the various textile materials, based on the dry textile substrate, are approximately:
These moisture contents are based on the weight of the dry textile material in accordance with the following equation:             (      %      )        =                                        m            v                    -                      m            d                                    m          d                    ⁢      100      ⁢      %        ,
where mv is the mass of the textile material in the moist or wet state and md is the mass of the textile material in the dry state under normal climatic conditions (T=20xc2x0 C.xc2x12xc2x0 C. and RH=65%xc2x12%).
If dyeing is carried out with a relative humidity of the fluid which is over 100%, there is free water in the system, which may cause rings to be formed in/on the textile material. There may even be a (polar) liquid film on the textile material, which makes transfer of the nonpolar dyestuff difficult.
Maintaining the relative humidity of the fluid in the range from 10 to 100% during the dyeing ensures that the textile material remains sufficiently moist and therefore is and remains sufficiently accessible for the uptake of the dyestuff. Furthermore, it is assumed that cotton with water forms a stronger nucleophilic reagent for fixation of the dyestuff than dry cotton.
Good fixation of the dyestuff is necessary if good washfastness and fastness to rubbing are to be obtained. For this purpose, the fixation is to take place by means of a nucleophilic reaction between the reactive groups of the dyestuff, on the one hand, and the fibre, on the other hand, for which reaction moisture is required and which reaction leads to the dyestuff being covalently bonded to the fibres of the textile material.
The way in which the relative humidity of the fluid is set and maintained in the range from 10-100% during the method is not critical. The possibilities include injection of water into the supercritical fluid, pretreatment of the textile material with water and extraction of water with the aid, for example, of molecular sieves or a condenser. The relative humidity can be measured using a capacitance meter.
The relative gas humidity is advantageously in the range from 50-100%, more preferably 60%, in particular is approximately 75%. It has been found that a relative humidity of the fluid of approximately 75% is advantageous for dyeing cotton and silk with a view to the dyeing and fixation. With a view to dyeing wool and viscose, the relative humidity of the fluid is advantageously in the range from 60-100%, although with a view to fixation a relative humidity of approximately 75% is once again preferred (T=115xc2x0 C. and p=260 bar).
Very good fixation for silk and wool is achieved with the aid of the method according to the invention, with 95-99% of the dyestuff being covalently bonded.
To obtain good fixation of the fibre-reactive disperse dyestuff which is used in the method according to the invention to cellulose-containing textile materials, it is advantageous to modify the reactive groups of the cellulose, as described, for example, in the abovementioned publication DE-A1-44 22 707, the substrate being modified prior to dyeing. A more general description of the modification of cotton is given by R. B. M. Holweg et al., xe2x80x9cReactive cottonxe2x80x9d, 18th IFATCC Congress 1999, Copenhagen, Sep. 8-10, 1999, pp. 58-64. For this modification, so-called aminating agents are used, which contain amino groups which react with and are thus fixed to the cellulose fibres via a covalent bond. For use in CO2, it is common to use aminating agents with primary and/or secondary amino groups, with which the reactive groups of the fibre-reactive disperse dyestuff can react and form a covalent bond. One example of an agent of this type is an aliphatic polyamine, available from Clariant, which gives secondary amino groups to the cellulose fibres. These aminating agents may also be small molecules, as described in U.S. Pat. No. 1,779,970.
It will be understood that, strictly speaking, it is not necessary for the relative humidity of the fluid to be maintained in the range from 10-100% for synthetic fibres, such as polyester and polyamide fibres, if present in the textile material, since these materials, on account of supercritical fluid being dissolved in the synthetic fibres, already have a relatively great accessibility for the dyestuff. It has been found that, when dyeing polyester using the method according to the invention, no unacceptable negative results are obtained for either dyeing or fixation. It is thus also possible for textile materials which are composed of a combination of natural fibres and synthetic fibres to be dyed simultaneously and under the same conditions, in particular with the same fluid and the same dyestuff.
For cellulose, the desired relative humidity of the fluid is advantageously set by subjecting the textile material to a moistening step for premoistening the textile material with an aqueous moistening agent prior to the dyeing. The aqueous moistening agent may, for example, be water, to which, if desired, additives are added.
The moistening step may, for example, be carried out using the padding method (foulard), in which the textile material is passed through a bath of the aqueous moistening agent and then the material is squeezed until the desired moisture content is reached.
The aqueous moistening agent may contain at least one auxiliary. In particular, the moistening agent may contain one or more agents which promote the accessibility of the fibres of the textile materials for the dyestuff, such as the preferred melamine, urea or thiodiethylene glycol.
Another auxiliary which can be considered for use in the moistening agent is a reaction-accelerating auxiliary for accelerating the reaction between the reactive disperse dyestuff and the textile material. Examples of these auxiliaries include, inter alia, pyridine or ammonium salts. These reaction accelerators often contain tertiary and quaternary amino groups. The abovementioned aminating agents may also be added to the moistening agent. Then, the textile material is dyed in accordance with the method according to the invention.
If desired, an agent for promoting the solubility of the fibre-reactive disperse dyestuff, such as acetone or ethanol, may be added to the supercritical fluid.
The dyeing conditions are selected on the basis of the textile material to be dyed. The temperature is usually in the range from 20-220xc2x0 C., preferably 90-150xc2x0 C. The pressure which is applied during dyeing should be at least sufficiently high for the fluid to be in the supercritical or almost critical state at the prevailing temperature. The pressure is usually in the range from 5xc3x97106-5xc3x97107 Pa (50-500 bar), more preferably 2xc3x97107-3xc3x97107 Pa (200-300 bar). As non-limiting examples, it is possible to mention a temperature of approximately 140xc2x0 C. and a pressure of approximately 2.5xc3x97107 Pa (250 bar) for dyeing cotton, while for wool a temperature of approximately 110xc2x0 and a pressure of approximately 2.5xc3x97107 Pa (250 bar) are preferred.
In addition to the padding method mentioned above, the moistening can also be carried out prior to the actual dyeing process, in which case the textile material is already in a dyeing vessel of the dyeing device used.
The moisture content can also be set during the dyeing itself, for example by injection of water or steam into the circulating fluid, to which, if desired, the necessary additives are added.
In this context, it should be pointed out that adding water as modifying agent in order to increase the polarity of the supercritical fluid for polar dyeing systems is described in DE-A-39 06 724, with the result that the solubility of the polar dyestuffs in the supercritical fluid is increased. However, in the method according to the present application the fibre-reactive disperse dyeing systems are apolar. Free water is present in a system of this type. By contrast, in the present invention the water has the function of ensuring the accessibility of the fibres for the dissolved dyestuff, so that the fibres are able to take up the dyestuff.
A dyeing device which is suitable for use in the method according to the invention is known in the specialist field and is described, for example, in an article entitled xe2x80x9cExperience with the Uhde CO2-dyeing plant on technical scalexe2x80x9d, Melliand International (3), 1998.
The reactive disperse dyestuffs which can be used in the method according to the invention may be selected from the dyestuffs which are mentioned, for example, in DE-A1-44 22 707, DE-A-20 08 811, U.S. Pat. Nos. 3,974,160, 5,498,267, 4,969,951, CH-A-564 515 and Japanese patent publications JP-3-247 665, JP 92/059 347, JP 91/035 342, JP 91/032 585 and JP 91/032 587.
The present invention also relates to a device for dyeing textile material in a supercritical or almost critical fluid, comprising a pressure vessel for holding the textile material which is to be dyed and means for supplying the fluid to the pressure vessel, wherein the device is also provided with regulating means for regulating the relative humidity of the fluid. During use of the device according to the invention, the relative humidity of the fluid is regulated by measuring the actual relative humidity with suitable measuring means, for example with a capacitance meter, and, in the event of deviation from the desired value, either adding moisture or extracting moisture. For this purpose, the regulating means may comprise supply means for supplying moisture and/or means for extracting moisture to/from the supercritical fluid. The supply means may be directly connected to the pressure vessel but may also be connected to the supply means for the supercritical fluid. Supply means of this type comprise, for example, injection means for the injection of steam. A condenser and a bed of molecular sieve material are examples of means for extracting moisture from the supercritical fluid, which may be arranged, for example, in the circulation pipe network of the supercritical fluid.
The present application is explained below with reference to the following examples. In these examples, the dyeing efficiency (measure of the fixation) is determined by washing at 95xc2x0 C. in accordance with the applicable ISO standard 105-C06, and determined with a boiling extraction with a mixture of water and acetone (volumetric ratio 4:1; t=0.5 h).